In order to prolong the life of a semiconductor laser element, it is necessary for an insulating layer to release efficiently to the outside heat generated by the semiconductor.
SiO.sub.2, polyimide resins or the like have been conventionally used for insulating layers of semiconductor laser elements. (See Hiroyuki Matsunami, Semiconductor Technology, Shoukoudo, pp. 214, or Applied Physics Letters, vol. 59, pp. 1,272 (1991).) However, SiO.sub.2 and polyimide resins have no sufficient thermal contacts with semiconductors, and their thermal conductivities are too weak to radiate heat efficiently. Therefore, conventional semiconductor laser elements having SiO.sub.2 or polyimide resins as insulating layers have poor endurance.
It was also impossible to apply n-type semiconductors anywhere above the active layers of conventional semiconductor laser elements. In conventional semiconductor laser elements, the active layers and the insulating layers are apart from each other. If an n-type semiconductor with high carrier mobility is applied between the active layer and the insulating layer, current is diffused in a horizontal direction and cannot be confined to the active layer. Therefore, in conventional semiconductor laser elements, n-type semiconductors are applied anywhere below the active layers while p-type semiconductors with a low carrier mobility are applied anywhere above the active layers. However, because of high top electrode resistance and the Schottky barrier between the top electrodes and the p-type semiconductors, the operating voltage of conventional semiconductor laser elements tends to become high, and heat is generated at the top electrodes of the elements.